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3.6 Percent Composition of Compounds 89 For example, for ethanol, which has the formula C 2 H s OH, the mass of each element present and the molar mass are obtained as follows: g Mass of C = 2 mot X 12.01 mot = 24.02 g g Mass of H = 6 mot X 1.008 mot = 6.048 g g Mass of 0 = 1 mot X 16.00 mot = 16.00 g Mass of 1 mol C 2 H s OH = 46.07 g The mass percent (often called the weight percent) of carbon in ethanol can be computed by comparing the mass of carbon in 1 mole of ethanol to the total mass of 1 mole of ethanol and multiplying the result by 100: mass of C in 1 mol C 2 H s OH Mass percent of C = X 100% mass of 1 mol C 2 H s OH 24.02 g ---=- X 100% = 52.14% 46.07 g The mass percents of hydrogen and oxygen in ethanol are obtained in a similar manner: mass of H in 1 mol C 2 H s OH Mass percent of H = f X 100% mass 0 1 mol C 2 H s OH 6.048 g --~ X 100% = 13.13% 46.07 g mass of 0 in 1 mol C 2 H s OH Mass percent of 0 = X 100% mass of 1 mol C 2 H s OH 16.00 g . ---=- X 100% = 34.73% 46.07 g Reality Check:
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Unformatted text preview: Notice that the percentages add up to 100.00%; this provides a check that the calculations are correct. EXAMPLE 3.9 Carvone is a substance that occurs in two forms having different arrangements of the atoms but the same molecular formula (C lO H I4 0) and mass. One type of carvone gives caraway seeds their characteristic smell, and the other type is responsible for the smell of spearmint oil. Compute the mass percent of each element in carvone. Solution Where are we going? To find the mass percent of each element in carvone What do we know? ./ Molecular formula, C lO H 14 What information do we need to find the mass percent? ./ Mass of each element (we'll use 1 mol carvone) ./ Molar mass of carvone...
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This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.

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